An X-ray detection apparatus that detects a radiation, especially an X-ray has been conventionally utilized in a wide field, such as an industrial nondestructive test, medical diagnostics, or scientific research such as structural analysis.
Among X-ray detection apparatuses, a high-sensitivity and a high-definition X-ray detection apparatus provided with an X-ray detection panel having a photodetector and a fluorescent layer has been known. The photodetector has a photoelectric conversion element section in which a plurality of photosensors and a plurality of thin-film transistors (TFTs) are two-dimensionally arranged. The fluorescent layer is directly formed on the photodetector. The fluorescent layer converts an X-ray into light that can be detected by the photoelectric conversion element section.
The X-ray detection panel is supported on one surface of a plate-shaped support member. A circuit board is supported on the other surface of the support member. The circuit board drives the X-ray detection panel. The X-ray detection panel and the circuit board are electrically connected to each other through a flexible circuit board.
When the X-ray detection apparatus is actuated, the circuit board generates heat. A part of the generated heat is radiated into air in a housing of the X-ray detection apparatus. However, a major part of the heat moves to a member having a lower temperature based on heat conduction.
Therefore, the heat generated in the circuit board is conducted to the support member that supports the circuit board. Further, the heat conducted to the support member is conducted to the X-ray detection panel having a lower temperature.
When the heat is conducted to the X-ray detection panel, a temperature of the X-ray detection panel increases, and an operation temperature becomes a high temperature. Then, a dark current of the photoelectric conversion element and a leak current of the TFTs increase and an amount of fixed noise fluctuates, which results in a problem causing unevenness in an image.
A calorific value of the circuit board is not uniform even when taking a partial view. The heat conductive property of the circuit board is not uniform even when taking a partial view either. Therefore, partial unevenness occurs in the temperature of the X-ray detection panel. Thus, in the X-ray detection panel, values of the dark current and the leak current partially fluctuate, and the fixed noise partially varies.
In regard to this problem, a method of cooling the circuit board or the X-ray detection panel by using a cooling device has been suggested (see, e.g., Jpn. Pat. Appln. KOkAI Publication No. 2005-283262 (page 6, FIGS. 1 to 2)). As the cooling device, although there is a cooler adopting a natural radiational cooling system, a peltier element or a cold-water circulation device is used in order to obtain sufficient cooling performance.
Further, a method of energizing the X-ray detection apparatus 24 hours before use to make uniform a variation of the leak current has been also suggested.